Amplifier system



July 10, 1945. F. K. FLOYD 2,379,897

AMPLIFIER SYSTEM Filed June 3, 1942 A I a @5 l||||||||||||||||||||| 1NVENTOR,

mama? A. I'Zoyal ATTORNEY.

Patented July 10, 1945 AMPIJFIER SYSTEM Frederick K. Floyd, Denver,0010., asslgnor to Claude M. Hathaway, doing business as HathawayInstrument Company Application June 3, 1942, Serial No. 445,5s2 11Claims. (01. 179-111) My invention relates to amplifier systems and moreparticularly to an amplifying system for direct currents or alternatingcurrents.

Heretofore whenever it was desired to obtain amplification of directcurrents or relatively low frequency alternating currents this was doneby using direct-coupled amplifiers. In such amplifiers the grid of onevacuum tube is connected to the plate of the preceding tube so thatchanges in a direct current potential on the grid of the input tube'willbe amplified by the system. Such amplifiers are used for low frequencyalternatin currents whenever it is desired to eliminate the phasedistortion which would be produced if the usual type of alternatingcurrent amplifier'were utilized. Many direct-coupled amplifiers however,particularly when usedfor amplifying direct currents or low frequencyalternating currents, have several disadvantages. One disadvantageresults from the fact that small changes in the filament, plate, andgrid supply voltages will produce erroneous indications in the outputcircuit. Still another disadvantage is the nature of the plate andfilament supply voltages that are required. Accordingly it would behighly desirable to provide an amplifying system capable of amplifyingdirect or alternating voltages or currents with a high degree of waveform reproduction without introducing errors caused by changes involtage of the source supplying the power to the amplifying system.Furthermore it would be desirable to provide an amplifying system whichwould operate to amplify direct currents or alternating currents fromsubstantially zero to an upper limit which would be determined only bythe physical limits of the component parts used in the amplifyingsystem.

Therefore it is an object of my invention to provide an improvedamplifying system for direct current or alternating current which has a,[high degree of wave form reproduction.

Another object of my invention is to provide an apparatus for and a.method of amplifying direct or alternating current without introducingerrors whenever the power source for the amplifying system varies involtage.

Still another object of my invention is to provide in an amplifyingsystem means for modulating an alternating current in accordance withdirect or alternating current which is to be amplified.

In accordance with my invention it is possible to overcome the abovementioned disadvantages of the prior art by providing an amplifyingsystem in which a generated alternating current is modulated inaccordance with the direct current or alternating current to beamplified, the modulated current is then amplified and subsequentlydemodulated to produce a current having a high degree of wave formreproduction corresponding to an amplification of the current to beamplified.

Other and further objects of my invention will become more readilyapparent by reference to the following description taken in connectionwith the accompanying drawing wherein Figure 1 is a circuit diagram of apreferred embodiment of my invention; Figure 2 at A and B showsalternatin and direct current voltages which are to be amplified;Figures 3 and 4 are explanatory of certain operations occurring withinthe amplifier; and Figure 5 illustrates the fidelity of wave formreproduction obtained by my invention.

Referring to Figure 1 of the drawing, there is.

shown a preferred embodiment of an amplifying system constructed inaccordance with my invention which has an input circuit II and an outputcircuit l2. The input circuit II is connected. between the grids andcathodes of a pair of vacuum tubes l3 and H the anodes of which areconnected to the outer extremities of a mid-tap winding ii of atransformer Hi. The two control electrodes or grids of the tubes l3 andM are connected to the one side of the input circuit II. The midpoint ofthe transformer l5 and the two cathodes of the-tubes l3 and I4 areconnected to the other side of the input circuit II. A secondtransformer winding I! of the transformer I6 is connected across animpedance IS. The impedance I8 is connected in a circuit having animpedance I9 provided with a sliding contact, an impedance 2|, andtransformer winding portions 22 and 23 of a transformer 24. Th'eimpedances l8, l9 and 2| together with the, transformer windings 22 and23 comprise a bridge circuit. One diagonal of the bridge extends fromthe common juncture of the windings 22 and 23 to an adjustable contact25 on the impedance l9. Betweenthis adjustable contact 25 and the commonjuncture of the windings 22 and 23 there is impressed an alternatingcurrent by means of a pair of the conductors 26. The alternating currentsupplied by the conductors 26 is preferably obtained from an altematins'current generator having a frequency higher than the frequency of anycurrent which is to be amplified and which would be connected to theinput circuit H. The transformer windings 22 and 23' which comprise twolegs of the bridge adjacent one diagonal of the bridge are coupled tothe transformer winding 21 of the transformer 24.

The transformer winding 21 is connected to the input of a vacuum tube28, which is provided with a cathode resistor 29. The anode of thevacuum tube 28 is connected through a plate resistor 3| to a suitablesource of plate voltage obtained from to the vacuum tubes 23 and 34.

' cult of a vacuum tube 34 which has a grid circuit coupling resistor 35and a cathode resistor 33. The anode of the vacuum tube 34 is connectedthrough primary winding 35- of a transformer 33 to theconductors 32which supply plate potential A second transformer winding 31 of thetransformer 33 is connected to a suitable full wave rectifier which maycomprise a bridge rectifier such as shown. The output of the full-waverectifier 38 is connected through a filter circuit having a. pair ofseries inductors 39 and II and a filter capacitor 42, to the outputterminals l2.

By referring to Figures 2, 3, 4, and 5 in connection with Figure 1. theoperation of the amplifying system will become readily apparent. If itis assumed that it is desired to amplify alternating current such asshown at A in Figure 2, this voltage appearing on the control electrodesof both of the vacuum tubes i3 and I4 will produce a variation in theeffect of the impedance I! which is a.

portion of one leg of a bridge circuit. Since the alternating currentsource connected to the terminals or conductors 26 supplies to thebridge circuit alternating current which appears across the leg of thebridge including the impedance 13, there will appear in winding I! oftransformer l3 alternating current potentials which energize thetransformer winding l5 so that alternating current voltages will appearbetween the cathodes and anodes-of the vacuum tubes l3 and M. The

' vacuum tubes l3 and I4 are so selected or arranged that they willoperate as half wave rectifiers. While by proper selection of vacuumtubes which will operate in the manner corresponding to Class Bamplifiers, the circuit may be as shown, it-will readily be appreciatedthat other vacuum tubes may be caused to operate in a similar manner byinserting between the oathodes and the mid-tap of the transformerwinding IS a suitable plate voltage. Since the vacuum tubes l3 and I4will operate as half wave rectifiers, the transformer It is loadedduring each half cycle of the alternating current appearing across thetransformer IT. This loading of the transformer winding l1 changes theeffect of the impedance l8 in one leg of the bridge. Thus the variationof the impedance l8 will be one which corresponds to a function of theplate resistance of the vacuum tubes I 3 and I I. This variation inplate resistance is determined by the voltage appearing across the inputcircuit l I.

In the absence of any input voltage appearing across the circuit II, thebridge is balanced by means of the adjustable contact 25 operating onthe impedance l9. Any variation of the position of the adjustablecontact 25 from the point of balance will cause a constant amount of thealternating current supplied from the alternating current generator bythe conductor 26, to appear across the transformer winding 21. By suchan arrangement therefore it is possible to control the percentage ofmodulation of the alternating current supplied to the bridge by theconductors 26. Therefore if it is assumed that the input circuit I I isbeing supplied with an alternating potential or alternating currentcorresponding to that former winding 21 will also correspondto therepresentation shown in Figure 3A, if it is assumed that the ordinatesnow have 'a greater value than heretofore. This current which is nowpassed through the full wave rectifier 33 will then produce currentacross the terminals ,GH corresponding to the representation shown inFigure 4. This in turn is transmitted through the filters to the outputterminals where the resultant current will be that represented in Figure5.

If new it is assumed that it is desired to amplify a direct currentwhich corresponds to the representation shown in Figure 2B, thealternating current potential appearing across the terminals CD and theterminals EF will be represented by curves similar to that shown inFigure 3B. The output of the rectifier 38 for such voltage will then berepresented by the curve shown in Figure 413. After passing through thefilters the voltage appearing across the output terminals l2is thatrepresented by Figure 5B.

It is to be understood that the amplifying system shown in Figure 1 issuitable for amplifying currents and voltages and that the terms alter-'nating current and direct current have been used in the description andexplanation in a broad sense so as to distinguish between two differenttypes of currents or voltages which may be amphfled by the system. a

From the above description and explanation of the amplifying system itwill be seen that in effect this system comprises a source ofalternating current having a frequency higher than that of any signalwhich is to be amplified. means for modulating such alternating current,an amplifier, a demodulator, and a filter. Due to the fact that theamplification is accomplished by the use of modulated alternatingcurrent having a high frequency as compared to the very low frequency ofthe input signal, the system operates with high stability so that anyvariations in the voltage of the source of power supplying filament orplate voltage will have substantially no detrimental effect on thesignal appearing across the output circuit. The frequency range overwhich the system will operate is determined by the selection of thecomponents and hence it is apparent that the system will amplify directcurrent, and alternating current beginning just above zero to anydesired frequency value. By selection of proper tubes and othercomponents the degree of amplification may be readily determinedregardless of I how low in intensity the signal or current to be shownin Fi ure 2A, there will appear across the amplified may be. I

While for the purpose of illustration and description there has beenshown a preferred embodiment of an amplifying system constructed inaccordance with my invention, it is to be understood that I do not wishto be limited thereto since obviously modifications may be made in thecircuit arrangements and in the instrumentalities employed withoutdeparting from the spirit and scope of my invention as set forth in theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A direct current or alternating current amplifying-system comprisinga bridge connected at diagonal points to a source of alternating currenthaving a frequency higher than the frequency of any alternating currentto be amplified, an im- .pedance element connected in one leg of thebridge, means including a vacuum tube rectifier for varying the efiectof said impedance element in accordance with the current to beamplified, an

amplifier having its input connected to adjacent legs of said bridge,and a rectifier connected to the output of said amplifier.

2. A system for amplifying direct or alternatin currents comprising abridge connected at diagonal points to a source of alternating currenthaving a frequency higher than that of any alternating current to beamplified, means including a controlled vacuum tube rectifier forvarying the effect of an impedance element connected in one leg of saidbridge in accordance with the current to be amplified, an amplifierconnected across the other diagonal of said bridge, and a rectifierconnected to the output of said amplifier.

3. A system for amplifying direct or alternating currents comprising abridge, a source of alternating current having a frequency higher thanthe frequency of any current to be amplified, said source beingconnected to one diagonal of said bridge, an amplifier connected to theother diagonal of said bridge, a rectifier connected to the output ofsaid amplifier, a vacuum tube rectifier connected to the impedance ofone leg of said bridge so that the impedance thereof will vary inaccordance with the variations of plate resistance of said tube, and aninput circuit for said tube for receiving direct or alternating currentsto'be amplified.

4. A system for amplifying direct or alternating currents comprising avacuum tube full wave rectifier having an input circuit for receivingdirect or alternating currents to be amplified, a bridge connected atone diagonal to a source of alternating current having a frequencyvhigher than that of any current to be amplified, means connected betweensaid vacuum tube and one leg of said bridge whereby the impedancethereof will be varied in accordance with variations in the amplifierconnected to the other diagonal of said bridge, and a rectifierconnectedto the output of said amplifier.

5. A system for amplifying direct or alternating currents comprising abridge connected at diago. nal points to a source of alternating currenthaving a frequency higher than the frequency of any current to beamplified, an impedance element connected to one leg of said bridge,means including a full wave controlled vacuum tube rectifier for varyingthe effect of said impedance in accordance with the current to beamplified, and an amplifier having its input circuit energized from twolegs of said bridge adjacent said diagonal.

6. The combination in a system for amplifying direct or alternatingcurrents comprising a bridge connected at one diagonal to a source ofalternating current having a frequency higher than that of any currentto be amplified. and means for varying the impedance in one leg of saidbridge in accordance with the current tobe amplified, said meansincluding a pair of vacuum tubes each having a control electrode, atransformer having a mid-tapped winding connected between the anodes andcathodes of said tubes and another winding connected tosaid leg of saidbridge, and an input circuit for the current to be amplified connectedbetween said control elecplitude of alternating current supplied from asource having a frequency higher than that of .any current to beamplified, a bridge circuit having one diagonal connected to saidsource, an output circuit energized from two legs on said bridgeadjacent said diagonal, and means for varying the impedance of anotherleg of said bridge in accordance with the current to be amplifiedcomprising a transformer having one winding con-,

nected to said latter leg and another winding connected between theanodes and the cathodes of a pair of vacuum tubes each having a controlelectrode, and a circuit connected to cathodes and said controlelectrodes for receiving current to be amplified, said cathodes beingconnected together, and said control electrodes being connectedtogether.

8. A direct current or alternating current amplifying system comprisinga bridge connected at one diagonal to a source of alternating currenthaving a frequency higher than the frequency of any alternating currentto be amplified, an alternating current amplifier connected to the otherdiagonal of said bridge, a rectifier connected to said amplifier, aninductance having a plurality of windings, one of said windings beingconnected across one leg of said bridge, and means connected to anotherwinding of said inductance for passing therethrough a direct currentproportional'to the current to be amplified thereby to proportionallyvary the effect of said inductance on said bridge.

9. A direct current or alternating current amplifying system comprisinga bridge connected at one diagonal to a source of alternating currenthaving a frequency higher than the frequency of any alternating currentto be amplified, an alternating current amplifier connected to the otherdiagonal of said bridge, a rectifier connected to said amplifier, aninductance having a plurality of windings, one of said windings beingconnected across'one leg of said bridge, the other of said windingscomprising a mid-tapped winding, a pair of vacuum tube rectifiers eachhaving an anode, a cathode and a control electrode, said anodes beingconnected to the outer terminals of said other winding, said cathodesbeing connected to the mid-tap of said winding, and an input circuitconnected between said cathodes and :both control electrodes.

10. A system for amplifying direct or altemating currents comprising abridge connected at one diagonal to a source of alternating current of afrequency greater than that of any alternating current to be amplified,an amplifier connected to the other diagonal of said bridge, aninductance having a plurality of windings, one of said windings beingconnected to one leg of said bridge, a full wave controlled vacuum tuberecticonnected to one leg of said bridge, said trans former having asecond winding provided with a midpoint, a pair of grid controlledvacuum tubes having their cathodes connected to the midpoint of saidwinding and their anodes each connected to one terminal of said winding,means connecting said grids together, and an input circuit for thecurrent to be amplified connected between said grids and said cathodes.

- FREDERICK K. FLOYD.

